The invention concerns the processing of materials and medical engineering and can be used for the processing of materials in dentistry, orthopedics, surgery, dermatology and other fields of medicine, for removal and destruction of hard and soft materials and tissues and for modification of properties of hard and soft materials and tissue surfaces.
The processing of hard dental tissues by simultaneous influence of laser radiation and the flow of abrasive particle is shown in U.S. Pat. No. 5,334,016, where a pneumatic system forms an air jet saturated by abrasive material and directs it on an object inside a patient""s mount. A disadvantage of this method is the necessity of delivering the abrasive particles through a pipe at very high speed, this causing loss of essential energy by the particles. Therefore, near the tissues, there are particles with kinetic energies that differ considerably, so that only some of them participate in the removal of tissues, enamel and dentin and the remaining particles are stored in the patient""s mouth, producing no useful effect. It can also be difficult to completely remove these particles, even with the help of an additional aspiration system.
The application of laser radiation in this prior art method results in a negligible increase in efficiency, since the air-abrasive flow and laser radiation do not interact, but independently produce additive influence so that the efficiency of laser processing is limited by the finite value of reflection and absorption indices of tissues. The removal, cutting, drilling and other specific methods of laser-tissue interaction are also accompanied in a number of cases with increased necrosis.
Another prior art method and apparatus for processing of materials including tissues uses particles of condensed substance (drops of liquid), which acceleration in the direction of a surface of the material being processed as a result of interaction with electromagnetic radiation directed to the processed surface. The main disadvantage of this technique is the insufficient hardness of liquid particles, so that, even at high speed, they cannot cut most materials, particularly hard materials such as metals, ceramics, enamel or dentin of tooth, with high efficiency.
A need therefore exists for methods and apparatus for the improved utilizing of both radiation and particles in the efficient and accurate processing of materials, including tissues.
In accordance with the above, this invention provides a method for processing a material having an outer surface, the term xe2x80x9cmaterialxe2x80x9d as used herein including biological tissue, and biological tissue being the material on which the invention is primarily adapted for use. However, the invention is by no means limited to use on biological tissue. The method includes distributing a substance containing abrasive particles in an area in front of at least a portion of the surface and irradiating both the substance and the portion of the surface with light selected to cause selective ablation of the substance sufficient to force the abrasion particles under a selected pulse against the portion of the surface. For some embodiments of the invention, the substance is the abrasive particles, the particles being of a size to be selectively ablated by the irradiation to force the particles against the surface. For this embodiment, the particles should have a size d greater than  greater than kxe2x88x921(xcex), d, the characteristic size of particle, being between 1 and 1000 xcexcm and k(xcex), the absorption index of the particle material at wavelength xcex, being between 105 cmxe2x88x921 and 102 cmxe2x88x921. These particles may for example be distributed into the area in front of the surface by airflow.
Alternatively, the substance may include the particles, each enclosed within a shell, the selective ablation being of the shell. For this embodiment, each shell should have a thickness xcex4 such that xcex4 greater than  greater than kxe2x88x921(xcex). For this embodiment, it is also preferable that 1 less than xcex4 less than 1000 xcexcm and that 105 cmxe2x88x921 greater than k greater than 102 cmxe2x88x921. The substance may be a suspension of the particles in a liquid, the liquid being selectively ablated by the light. The distributing step distributes the suspension to the surface to cool the material and the irradiating step irradiates a small portion of the surface, particles being forced for the most part only against such small portion to cause the processing thereof. The shell may be substantially completely ablated by the irradiation thereof so as not to interfere with the action of the particles on the surface.
For still another embodiment of the invention, the substance is a substantially solid body containing the particles, a component of the body being selectively ablated by the light, and the distributing step includes the step performed throughout the processing of the material of maintaining a portion of the body between the light and the portion of the surface being processed. The solid body may be formed as a suspension of the particles in a substantially solid binder, the binder for example being the component selectively ablated by the light, or the solid body may be formed of the particles processed, for example by sintering or under pressure to adhere in the desired shape.
The substance may be distributed to the area in front of the surface for a duration xcfx84, the light having an energy density E near the surface such that xcfx84 less than  less than d2/4xcex1 and E greater than  greater than kxe2x88x921(xcex)xcfx81Q. E may be, for example, between 10xe2x88x921 and 104 j/cm2.
The irradiation may be performed continuously or may be performed as a sequence of time-spaced light pulses. Similarly, the distribution of substance may be by a series of distribution pulses. The distribution pulses may be synchronized with the light pulses or may occur before each light pulse, the duration of the distribution pulses being less than the time between light pulses in the latter case. A distribution pulses may also have a repetition rate which is less than that for the light pulses.
The invention also includes apparatus for processing a material, as previously defined, having an outer surface, which apparatus includes a mechanism selectively providing a substance containing abrasive particles in an area in front of at least a portion of the surface to be processed, a light source, and a system for selectively directing light from the source to irradiate both the substance and the portion of the surface, the source and the system being selected to cause selective ablation of the substance in response to irradiation thereof sufficient to force abrasive particles under a selected pulse against the portion of the surface. The light source may for example be a laser, an incandescent lamp or a flash lamp. The system for selectively directing light may include a control which operates the source in a selected pulse mode and an optical system directing light from the source to a tip, the mechanism selectively providing the substance through the tip to the area and the tip being adapted to direct light through the area to the portion of the surface. The substance may also be provided to the area by the mechanism as a series of distribution pulses. The distribution pulses may be provided in synchronism with the light pulses from the source or the distribution pulses may occur before each light pulse, the duration of the distribution pulses being less than the time between light pulses. The distribution pulses may have a repetition rate which is less than the repetition rate for the selected pulse mode in which the source is operated. Alternatively, the control may operate the source continuously.
The mechanism may be operated to distribute the substance to the area for a duration xcfx84, and the source may deliver light radiation having an energy density E near the surface of the material such that 10xe2x88x921 less than E less than 104 j/cm2. In this case, E is preferably between 10xe2x88x921 and 104 j/cm2.
For some embodiments, the substance is the abrasive particles and the mechanism includes a source of the particles, a carrier for delivering the particles to the area, and a control for operating on at least one of the carrier and the source to provide a controlled delivery of particles to the area, the particles being of a size to be selectively ablated by light irradiation directed thereat from the source. The carrier may be delivered under pressure to an air pipe under control of a valve operated by the control, the particles being delivered from a source thereof to the air pipe to be carried therethrough by air to the area in front of the material surface. Alternatively, the carrier may be a liquid, the substance being a suspension of the particles in the liquid, the liquid being selectively ablated by the light. In this case, particularly where the material is biological tissue, the mechanism may be controlled to deliver the suspension to the surface to cool the material prior to the system applying light to the substance to ablate the liquid, forcing the particles for the most part only against a small portion of the surface irradiated by the light to cause processing of material at the portion.
For some embodiments of the invention, the substance is in the form of a substantially solid body containing the particles, an indexing mechanism being provided for both supporting and maintaining the body in an area between the light and the portion of the surface to be processed. The solid body may be a suspension of the particles in a substantially solid binder, the binder for example being selectively ablated by the light, or the particles may be processed to adhere in a desired shape, for example by sintering, pressure or the like.
The substance may be sapphire particles suspended in water, with a light source for such substance being, for example, an ER-laser. Where a laser is used as the light source, the light source may for example be CO2 laser or an excimer laser. For one embodiment, a neodymium laser is used with carbon particles as the substance. Where the material being processed is biological tissue, the particles are preferably biologically safe materials such as hydroxyapatite, carbon, silicon or ice.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more detailed description of preferred embodiments as illustrated in the accompanying drawings, the same reference numerals being used for common elements in all the drawings.